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TI 99 expansion port question...


firebottle
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I would say that it all has something to do with the environments the machine has been in over the years and how often you connect things to it. The bare copper oxidizes a lot faster than the solder does. You might want to just coat the fingers with a new layer of thin solder, just to keep oxidation down. . .you are speaking of the fingers that are part of the circuit card and not the protective metal shell fingers, correct?

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I would say that it all has something to do with the environments the machine has been in over the years and how often you connect things to it. The bare copper oxidizes a lot faster than the solder does. You might want to just coat the fingers with a new layer of thin solder, just to keep oxidation down. . .you are speaking of the fingers that are part of the circuit card and not the protective metal shell fingers, correct?

 

Correct.

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The solder adhered to the copper etches on the edge connector shouldn't "flake off," since the lead in solder makes it somewhat flexible- not brittle. Visible scratches, caused by the (female) connector pins when attached, when mated and de-mated are normal. Depending on the amount of copper showing as the edge connector wears down, reliability of the system can be compromised.

 

I recommend always trying the easiest, most non-invasive repair method first. (The "Do No Harm" rule applies here.)

 

In the case of edge connectors, clean them with a pencil eraser to remove any oxidation. Then view the etch contacts under magnification to try to judge the depth of the scratches. If they're greater than 50%, re-flow the etch solder with a minimum amount of small diameter, (we're not sweating plumbing joints here) rosin core solder with a healthy amount of paste or liquid flux applied (NEVER ACID FLUX!!) to ensure adequate solder wetting.

 

Apply the solder at the inside of the pad, and draw the solder outward, by pulling the tip toward the edge. Solder only sticks to clean, hot, metal, so it will want to follow the heat if your technique is right as far as having enough flux, the right amount of solder, and the proper tip dwell time.

 

Don't flow adjacent pads in succession; skip a few over and keep jumping around. Excessive heat will break down the epoxy securing the pads to the board, and then you have a harder problem to overcome. The trick is to use the right size solder tip, the proper amount of heat, and the minimum amount of dwell time to flow the solder the length of the connector pad. If you've never attempted this, I'd recommend experimenting on a junk board to get your technique refined. It isn't hard, you just don't want to train on your good stuff first.

 

Clean the connector with IPA and an acid brush, (common, small horse-hair brushes) cut diagonally near the joint where the horse hair meets the rolled, metal handle. (This gives you both short/stiff and longer/soft bristles to remove the flux.) The sooner you clean the flux after application, the easier it is to remove. Wait a day and try cleaning if you want to test this. . .

 

After that, ensure an even flow by using the right-sized solder wick (I use Chemtronics Soder-Wick, with flux added) and drag the (hot) braid length-wise toward the outside of the edge connector, skipping around to minimize heat, just like before, when applying solder. I like to apply a little liquid flux to the wick, just to supplement the dry flux embedded in the braid. Clean thoroughly (no sticky residue remaining) when done.

 

Following these tips will give you added years of reliability and enjoyment of your system.

 

CC

Edited by CC Clarke
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